ISPROP Tests if a property is present

    I=ISPROP(DATA,PROP)
    [I,TYPE]=ISPROP(DATA,PROP)

 INPUT
    DATA    Data set
    PROP    Property name

 OUTPUT
    I       Logical value
    TYPE    string property type ('sample','feat' or 'data')

 DESCRIPTION
 ISPROP returns 1 if the property PROP exists in DATA, and 0 otherwise.
 In the second output argument, ISPROP returns the property type.